no document type declaration; implying %1

Cause:

The checked page did not contain a document type ("DOCTYPE") declaration. The Validator has tried to validate with a fallback DTD, but this is quite likely to be incorrect and will generate a large number of incorrect error messages. It is highly recommended that you insert the proper DOCTYPE declaration in your document -- instructions for doing this are given above -- and it is necessary to have this declaration before the page can be declared to be valid.

Example:

textexample textexample

Bad:
textexample textexample
Good:
textexample textexample

Solution:

textexample textexample

References: